In the 1920s, State Highway 111 followed today's Route 66 between today's Route 10 (Milldale) and Route 2 (Marlborough). In 1930, it was even co-signed with the old New England Interstate Route 3 to Waterbury.

The modern Route 111, commissioned in 1932, extended 7.75 miles from Route 25 in Trumbull (intersection of Main Street and Monroe Turnpike) to Route 34. Main Street south of this intersection was part of Route 25.

When the 25 freeway opened on June 1, 1982, Route 111 was extended south along former Route 25 to end at Route 15.

Further widening in Monroe

A reconstruction of Route 111 in Monroe was proposed, to increase safety and capacity without radically changing its character. Probably minor widening is planned. The project is in the 1995 Greater Bridgeport and Valley Transportation Improvement Program (TIP), slated for a 2007-2015 time frame. In April 2003, Congressman Christopher Shays requested $10 million in federal funds toward this project.

The state had developed a widening plan in the mid-1990s, addressing a 2.29-mile segment from Purdy Hill Rd. to Fan Hill Rd. Many residents opposed the plan, fearing it would detract from the town's rural charm.

As of mid-2005, a new plan was proposed:

• From Purdy Hill Rd. to vic. of Elm St.: four 12-foot travel lanes with 4-foot shoulders. Turn lanes at several commercial properties.
• From vic. Elm St. to Cross Hill Rd.: two lanes, with center lane for left turns.
• From Cross Hill Rd. to Fan Hill Rd.: two 12-foot lanes with 4-foot shoulders; minor widening for a uniform width, and slight realignment for safety and visibility.
• At Route 110: modify to a straight T-intersection and install a traffic signal.

Estimated cost was $10 million. In August 2005, Congressman Christopher Shays secured $1.2 million in federal funding for the work. Residents and officials seem happier with the compromise plan.

Roundabout at Route 110

In July 2018, a roundabout with Route 110 in Monroe was constructed, replacing a traffic signalled intersection with a poor safety record.